JP6468250B2 - Image forming apparatus - Google Patents

Description

  The present invention relates to an image forming apparatus including a photosensitive drum.

  An electrophotographic image forming apparatus includes a photosensitive drum on which a toner image is formed by a developing device. The toner image formed on the photosensitive drum is primarily transferred to the transfer belt by the transfer device while the photosensitive drum is rotated, and then secondarily transferred to the printing paper. In this type of image forming apparatus, a transmission member is provided at the end of the photosensitive drum in the longitudinal direction, and the rotational driving force is input to a gear formed integrally with the transmission member, thereby rotating the photosensitive drum. The force is transmitted to the photosensitive drum, and the photosensitive drum is rotated. 2. Description of the Related Art Conventionally, there has been known an image forming apparatus having, as the transmission member, a flange that comes into contact with an end portion of a photosensitive drum, and a gear having teeth formed on an outer peripheral surface of a protruding portion that protrudes axially outward from the flange. (See Patent Document 1).

JP 2000-89608 A

  However, in the conventional image forming apparatus, the outer diameter of the gear of the transmission member may be larger than the outer diameter of the photosensitive drum. In this case, when the photosensitive drum is pulled out along the longitudinal direction from the image forming apparatus for replacement or maintenance, the gear contacts the surface of the transfer belt during the pulling process, and streaks or scratches are formed on the surface of the transfer belt. There is a risk that In addition, a lubricant is applied to the gear to facilitate drive transmission. However, when the photosensitive drum is pulled out with the lubricant applied to the gear, the lubricant is applied from the gear to the surface of the transfer belt. There is a risk of adhesion.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to form an image that can reduce the fact that the gear provided at the end of the photosensitive drum contacts the transfer belt and contaminates or damages the transfer belt. To provide an apparatus.

  An image forming apparatus according to an aspect of the present invention includes a transfer belt, a photosensitive drum, and a transmission member. The transfer belt is provided in the apparatus main body. The transfer belt is provided in the apparatus main body. The transfer belt has a transfer surface onto which a toner image is transferred. The photosensitive drum is detachably provided in the apparatus main body. The photosensitive drum is formed in a cylindrical shape whose axial direction is the insertion direction with respect to the apparatus main body. The photoconductive drum faces the transfer surface of the transfer belt in a mounted state mounted on the apparatus main body. The transmission member is attached to the end of the photosensitive drum on the insertion direction side, and transmits the input rotational driving force to the photosensitive drum. The transmission member has a flange and a gear. The flange is formed to have an outer diameter larger than the outer diameter of the photosensitive drum. The gear protrudes in the insertion direction from the flange, and has teeth that receive the rotational driving force on an outer peripheral surface. The gear is formed to have an outer diameter larger than the outer diameter of the photosensitive drum and smaller than the outer diameter of the flange.

  According to the present invention, it is possible to prevent the gear provided at the end of the photosensitive drum from coming into contact with the transfer belt and contaminating or damaging the transfer belt.

FIG. 1 is a diagram illustrating a configuration of an image forming apparatus according to an embodiment of the present invention. FIG. 2 is a cross-sectional view illustrating a configuration of an image forming unit included in the image forming apparatus. FIG. 3 is a view showing a support structure of the photosensitive drum and the developing roller when viewed from the direction of arrow III in FIG. 4A and 4B are cross-sectional views showing the configuration of the transmission member provided at the end of the photosensitive drum. 5A and 5B are cross-sectional views showing the configuration of the transmission member provided at the end of the photosensitive drum.

  Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. The following embodiment is an example embodying the present invention, and does not limit the technical scope of the present invention. In the following description, the vertical direction 6 is defined in a state where the image forming apparatus 10 is installed on a flat support surface (the state shown in FIG. 1). Also, the front-rear direction 7 is defined with the left side of the paper surface of FIG. 1 as the front side (front side) of the image forming apparatus 10. Further, a left-right direction 8 (direction perpendicular to the paper surface of FIG. 1) is defined when the image forming apparatus 10 of FIG. 1 is viewed from the front. Accordingly, the front side is the right side of the image forming apparatus 10 and the back side is the left side with respect to the paper surface of FIG.

  The image forming apparatus 10 is an apparatus having at least a printing function. As shown in FIG. 1, the image forming apparatus 10 is a so-called tandem type color printer. The image forming apparatus 10 prints an image on a sheet-like printing paper using a developer containing toner. The image forming apparatus 10 only needs to have a printing function. For example, the image forming apparatus 10 may be an image forming apparatus such as a multifunction machine having a plurality of functions including the printing function, a FAX apparatus, and a copying machine. Good.

  As shown in FIG. 1, the image forming apparatus 10 mainly includes four image forming units 21, an intermediate transfer unit 22, a paper feeding cassette 25, a fixing device 26, a secondary transfer device 27, and an optical scanning device. 24 and four toner containers 50. These components are provided in the apparatus main body 28 as a casing constituting an external frame (not shown), an internal frame (not shown) and the like of the image forming apparatus 10.

  The four image forming units 21 are disposed below the intermediate transfer unit 22 inside the apparatus main body 28. Each image forming unit 21 executes an image forming process for forming an image on printing paper based on a so-called electrophotographic system. Specifically, each image forming unit 21 prints an image on printing paper based on image data input from the outside via a network communication unit (not shown). The image forming unit 21 includes a photosensitive drum 11, a charging device 14, a developing device 12, a primary transfer device 13, a cleaning device 15, and the like.

  The photoconductive drum 11 holds a toner image to be transferred onto the printing paper. The photosensitive drum 11 is provided so as to face the transfer surface of the transfer belt 23 of the intermediate transfer unit 22. The photosensitive drum 11 carries a toner image by the developing device 12 during the image forming process. The photosensitive drum 11 carries a toner image corresponding to the electrostatic latent image formed on the outer peripheral surface thereof while being driven to rotate. The photosensitive drum 11 is formed in a cylindrical shape, and a thin layer using an amorphous silicon (a-Si) material is formed on the surface of an aluminum tube.

  The intermediate transfer unit 22 is provided above the image forming unit 21 inside the apparatus main body 28. A driving pulley 31 and a driven pulley 32 are provided at both ends in the front-rear direction 7 of the intermediate transfer unit 22. The intermediate transfer unit 22 includes a transfer belt 23. The transfer belt 23 is supported so as to hang over the driving pulley 31 and the driven pulley 32. Thereby, the surface (transfer surface) of the transfer belt 23 extends in the front-rear direction 7 in a horizontal state. The transfer belt 23 can move (run) in the direction of the arrow 19 in a state where the surface thereof is in contact with the surface of each photosensitive drum 11. The toner image transferred from the photosensitive drum 11 is held on the surface of the transfer belt 23.

  The secondary transfer device 27 transfers the toner image composed of a plurality of colors transferred to the transfer belt 23 onto the printing paper. The printing paper on which the toner image has been transferred is conveyed to the fixing device 26. The fixing device 26 fixes the toner image transferred to the printing paper on the printing paper by heat. The fixing device 26 includes a heating roller 26A that is heated to a high temperature, and a pressure roller 26B that is disposed to face the heating roller 26A. The printing paper conveyed to the fixing device 26 is conveyed while being nipped by a predetermined urging force at the nip portion between the heating roller 26A and the pressure roller 26B, so that the toner image is fused to the printing paper. Thereafter, the printing paper is discharged to a paper discharge tray 29 provided on the upper portion of the apparatus main body 28.

  The four toner containers 50 are disposed above the intermediate transfer unit 22. The four toner containers 50 are arranged in a line along the transfer belt 23 in the front-rear direction 7 inside the apparatus main body 28. The toner container 50 is configured to supply toner to the corresponding color developing device 12.

  The optical scanning device 24 is provided below the image forming unit 21, specifically, between the image forming unit 21 and the paper feed cassette 25. The optical scanning device 24 includes a laser light source that emits laser light of each color, a polygon mirror as a scanning member that scans the laser light, a motor that rotationally drives the polygon mirror, a mirror that emits the scanned laser light, and the like. . The optical scanning device 24 irradiates the photosensitive drum 11 of each image forming unit 21 with laser light based on the input image data of each color. Thereby, an electrostatic latent image is formed on each of the photosensitive drums 11.

  FIG. 2 is a cross-sectional view illustrating a configuration of the image forming unit 21. The developing device 12 develops the electrostatic latent image with toner by a developing method in which toner is electrostatically attached to the photosensitive drum 11 in a non-contact state. As shown in FIG. 2, the developing device 12 includes a housing 53, a first stirring screw 54, a second stirring screw 55, a magnetic roller 56, a developing roller 57, a rotating roller 58, and the like. A two-component developer containing toner is accommodated in the bottom of the housing 53, and this developer is conveyed while being stirred by the first stirring screw 54 and the second stirring screw 55. The magnetic roller 56 draws the developer from the second stirring screw 55 by the built-in magnetic pole, and causes only the toner contained in the developer to adhere to the surface of the developing roller 57. The developing roller 57 is provided with a predetermined gap from the outer peripheral surface of the photosensitive drum 11. The toner held on the developing roller 57 is attached to the electrostatic latent image on the photosensitive drum 11 by the potential difference applied between the developing roller 57 and the photosensitive drum 11.

  As shown in FIG. 3, the rotating rollers 58 are provided at both ends of the rotating shaft 57 </ b> A of the developing roller 57 in the axial direction. The rotating roller 58 is pivotally supported by the rotating shaft 57A in a state where the rotating roller 58 is pressed to both ends of the outer peripheral surface of the photosensitive drum 11 with a predetermined urging force F (see FIG. 2). The radius of the rotating roller 58 is larger than the radius of the developing roller 57. Specifically, the radius of the rotating roller 58 is larger than the radius of the developing roller 57 by the gap between the developing roller 57 and the photosensitive drum 11. For this reason, when the rotary roller 58 contacts both ends of the photosensitive drum 11, the developing roller 57 is positioned at a position spaced apart from the photosensitive drum 11 by the predetermined gap. As a configuration for applying the urging force F to the photosensitive drum 11 from the rotating roller 58, for example, a configuration in which both ends of the rotating shaft 57A are urged toward the center of the photosensitive drum 11 using an elastic member such as a spring. Is applicable.

  The developing roller 57 is separated from the photosensitive drum 11 by a conventionally known separation mechanism (not shown) in order to facilitate the removal of the drum unit 17 when the later-described drum unit 17 is pulled out from the apparatus main body 28.

  As shown in FIG. 2, the cleaning device 15 removes the toner remaining on the photosensitive drum 11. The cleaning device 15 is disposed on the rear side of the photosensitive drum 11. The cleaning device 15 is provided for each photosensitive drum 11. The cleaning device 15 includes a cleaning blade 61, which is a cleaning member, a cleaning roller 62A, a recovery roller 62B, a screw member 63, and a housing 64. The cleaning blade 61, the cleaning roller 62A, and the collection roller 62B are supported by the housing 64. The cleaning blade 61, the cleaning roller 62 </ b> A, and the recovery roller 62 </ b> B have substantially the same length as the photosensitive drum 11. The tip of the cleaning blade 61 is disposed in contact with or close to the surface of the photosensitive drum 11.

  The cleaning roller 62 </ b> A and the recovery roller 62 </ b> B are rotatably supported in the housing 64. When the rotational driving force is input to the support shaft of the cleaning roller 62A, the cleaning roller 62A rotates. The cleaning blade 61 removes the toner remaining on the surface of the photosensitive drum 11 after the transfer by the primary transfer device 13 when the photosensitive drum 11 is rotated. The removed toner (hereinafter referred to as “waste toner”) moves to the bottom of the housing 64 by the action of gravity or the rotational force of the cleaning roller 62A. The waste toner that has moved to the bottom of the housing 64 is conveyed by the rotating screw member 63. A discharge port (not shown) is formed in the side wall of the right end portion of the housing 64. Waste toner is discharged to the outside through the discharge port. The waste toner adhering to the surface of the cleaning roller 62A is scraped off by the recovery roller 62B.

  In the present embodiment, the photosensitive drum 11 is supported by the housing 64, and the cleaning device 15 and the photosensitive drum 11 are integrally configured. In other words, the photosensitive drum 11 and the cleaning device 15 are unitized as a drum unit 17 by mounting the members of the photosensitive drum 11 and the cleaning device 15 on the housing 64.

  As shown in FIG. 2, the charging device 14 is provided inside the housing portion 64 </ b> A at the bottom of the housing 64. The housing 64 is configured to be detachable from the support frame 70 provided in the image forming unit 21. Specifically, a rail 68 that is slidably supported by the support frame 70 is provided at the bottom of the housing portion 64 </ b> A of the housing 64. The support frame 70 is provided in the apparatus main body 28, and a rail guide 70A through which the rail 68 is inserted is provided. The rail 68 is inserted into the rail guide 70A when the drum unit 17 is inserted from the right side surface of the apparatus main body 28 to the left side (the back side in the drawing in FIG. 2) in order to mount the drum unit 17 on the apparatus main body 28. In a state where the rail 68 is inserted into the rail guide 70A, the housing 64 is fixed so that it cannot move in the vertical direction 6 and the front-rear direction 7. When the drum unit 17 is removed from the apparatus main body 28, the drum unit 17 is pulled rightward (front side in FIG. 2) while the drum unit 17 is attached to the apparatus main body 28. Move to. Thereby, the drum unit 17 can be removed from the right side surface of the apparatus main body 28.

  As shown in FIG. 3, a first transmission gear 65 is provided at one end (right side) of the photosensitive drum 11. The first transmission gear 65 is fitted into the inner hole at the right end of the photosensitive drum 11 and is fixed (connected) integrally.

  A second transmission gear 75 (an example of a transmission member of the present invention) is provided at the other end (left side) end of the photosensitive drum 11. The second transmission gear 75 is attached to the end of the photosensitive drum 11 on the side of the insertion direction 8 </ b> A that is inserted into the apparatus main body 28 when the drum unit 17 is attached to the apparatus main body 28. The second transmission gear 75 transmits a rotational driving force input from a driving source such as a motor (not shown) to the photosensitive drum 11. The second transmission gear 75 is fitted into the inner hole of the side end portion of the photosensitive drum 11 and fixed (connected) integrally.

  A shaft hole is formed at the center of each of the first transmission gear 65 and the second transmission gear 75. The rotation shaft 67 of the photosensitive drum 11 is inserted through the shaft hole of the first transmission gear 65 and the shaft hole of the second transmission gear 75. A sliding clearance is provided between each shaft hole and the rotation shaft 67 so that the rotation shaft 67 can rotate.

  The housing 64 of the drum unit 17 includes support portions 71 and 72 that rotatably support the photosensitive drum 11. The photosensitive drum 11 is supported by the support portions 71 and 72. As shown in FIG. 3, support portions 71 and 72 are provided at both ends in the longitudinal direction of the housing 64. A bearing hole 71 </ b> A is formed in the support portion 71, and a bearing hole 72 </ b> A is formed in the support portion 72. Each of the bearing holes 71A and 72A is a portion through which the shaft portion 65C of the first transmission gear 65 and the shaft portion 94 of the second transmission gear 75 are inserted. The shaft portion 65C of the first transmission gear 65 is rotatably supported by the bearing hole 71A via the bush member 80. Further, the shaft portion 94 of the second transmission gear 75 is rotatably supported in the bearing hole 72A via the bush member 80. In addition, in FIG. 3, although the support parts 71 and 72 are shown, the whole housing 64 is not shown.

  By the way, when the drum unit 17 is pulled out from the apparatus main body 28, the gear portion 93 may come into contact with the transfer surface of the transfer belt 23 in the pulling process. When the gear portion 93 comes into contact with the transfer belt 23, the transfer surface may have a streak-like trace or may be damaged. The traces and scratches cause the toner image held on the transfer surface to be disturbed. In addition, a lubricant is applied to the gear portion 93 in order to facilitate drive transmission. However, when the gear portion 93 comes into contact with the transfer surface of the transfer belt 23 and the lubricant adheres to the transfer surface, the transfer surface. The toner image is disturbed, and the image formation is adversely affected. Such a problem may occur even when the developing roller 57 is separated from the photosensitive drum 11 by the separation mechanism. In the present embodiment, in order to solve such a problem, the second transmission gear 75 is configured as described below.

  Hereinafter, the configuration of the second transmission gear 75 will be described in detail with reference to FIGS. 4 and 5.

  FIG. 4 is a view showing a cross-sectional structure of the second transmission gear 75 when it is cut along a line connecting the rotation shaft 57A of the developing roller 57 and the rotation shaft 67 of the photosensitive drum 11. As shown in FIG. 4A is a cross-sectional view when the drum unit 17 is mounted on the apparatus main body 28 (mounted state), and FIG. 4B is a view when the drum unit 17 is slightly pulled out from the mounted state. FIG. In FIG. 4, the housing 64 and the rotating shaft 67 are not shown.

  As shown in FIG. 4A, the second transmission gear 75 includes a fitting portion 91, a flange 92, a gear portion 93, and a shaft portion 94.

  The fitting portion 91 is a fixed portion that is fitted into the inner hole of the left end portion of the photosensitive drum 11. The fitting portion 91 is a cylindrical portion that protrudes from the flange 92 in the axial direction of the photosensitive drum 11. By fitting the fitting portion 91 into the inner hole of the photosensitive drum 11, the second transmission gear 75 is fixed to the left end portion of the photosensitive drum 11.

  The flange 92 is an annular protruding rib that is formed on the outer peripheral surface of the photosensitive drum 11 and protrudes outward (in a direction away from the rotation shaft 67) from the outer peripheral surface. The flange 92 is formed to have an outer diameter D2 that is larger than the outer diameter D1 of the photosensitive drum 11.

  A gear portion 93 is provided so as to protrude from the flange 92 in the insertion direction 8A. A gear composed of a plurality of teeth to which the rotational driving force is input is formed on the outer peripheral surface of the gear portion 93. The gear portion 93 is a so-called spur gear having teeth formed on the outer peripheral surface. The outer diameter D3 of the gear portion 93 is larger than the outer diameter D1 of the photosensitive drum 11 and smaller than the outer diameter D2 of the flange 92.

  The shaft portion 94 is a cylindrical member that protrudes from the gear portion 93 in the insertion direction 8A. The shaft portion 94 is inserted into the bearing hole 72A of the support portion 72 and is rotatably supported.

  FIG. 5 is a view showing a cross-sectional structure of the second transmission gear 75 when cut along a vertical line passing through the center of the photosensitive drum 11. 5A is a cross-sectional view when the drum unit 17 is mounted on the apparatus main body 28 (mounted state), and FIG. 5B is when the drum unit 17 is slightly pulled out of the mounted state. FIG. In FIG. 5, the housing 64 and the rotating shaft 67 are not shown.

  As shown in FIG. 5A, the flange 92 is not in contact with the belt end 23A of the transfer belt 23 on the insertion direction 8A side in the mounted state. On the other hand, as shown in FIG. 5B, the flange 92 contacts the belt end portion 23A in the process in which the drum unit 17 is pulled out from the apparatus main body 28. As described above, the outer diameter D2 of the flange 92 is larger than the outer diameter D1 of the photosensitive drum 11. Therefore, when the drum unit 17 is pulled out, the flange 92 comes into contact with the belt end portion 23A, and when the drum unit 17 is further pulled out, the transfer belt 23 is pushed upward and rides on the top portion (radial end portion) of the flange 92. In this case, since the outer diameter D <b> 2 of the flange 92 is larger than the outer diameter D <b> 3 of the gear portion 93, the gear portion 93 does not contact the transfer surface of the transfer belt 23. Further, since the flange 92 lifts the transfer belt 23 while the drum unit 17 is removed from the apparatus main body 28, the gear portion 93 does not contact the transfer surface of the transfer belt 23 during this time.

  The flange 92 has an inclined surface 92A that is inclined with respect to the belt end 23A in the mounted state. Specifically, in the flange 92, an inclined surface 92A is formed at a position facing the belt end 23A in the mounted state. The inclined surface 92 </ b> A is formed by chamfering the top corner of the flange 92. In the process in which the drum unit 17 is pulled out, the inclined surface 92A smoothly guides the belt end 23A to the top of the flange 92. Thereby, when the flange 92 contacts the belt end portion 23A in the process of pulling out the drum unit 17, the burden on the belt end portion 23A is reduced.

  As shown in FIG. 2, a film member 97 (an example of the elastic member of the present invention) is provided at a position closer to the transfer belt 23 than the developing roller 57. The housing 53 of the developing device 12 has an opening 12 </ b> A for exposing the developing roller 57 toward the photosensitive drum 11. In the housing 53, the upper wall 53A located above the developing roller 57 extends toward the opening 12A and reaches the edge of the opening 12A. In the present embodiment, the film member 97 is fixed to the back surface (inner side surface) of the upper wall 53 </ b> A and extends from the opening 12 </ b> A toward the photosensitive drum 11. The extended end extends beyond the top of the flange 92 and reaches the vicinity of the outer peripheral surface of the photosensitive drum 11. Various methods such as adhesion, screwing, pressure bonding, and welding can be applied to the film member 97.

  Here, since the film member 97 extends from the opening 12 </ b> A toward the photosensitive drum 11, the floating toner is prevented from entering the gap between the developing roller 57 and the photosensitive drum 11.

  The film member 97 is a resin plate member made of synthetic resin. As the synthetic resin, a PET resin or the like is used. The film member 97 has elasticity that bends when receiving an external force and returns to its original state when the external force is released. The film member 97 is formed in a rectangular shape that is long in the longitudinal direction of the housing 53 (direction perpendicular to the paper surface of FIG. 2).

  As shown in FIG. 4A, the film member 97 is not in contact with the flange 92 of the second transmission gear 75 in the mounted state. On the other hand, as shown in FIG. 4B, in the process in which the drum unit 17 is pulled out from the apparatus main body 28, the flange 92 contacts the film end portion 97A on the side of the insertion direction 8A in the film member 97. As described above, the extending end of the film member 97 reaches the vicinity of the outer peripheral surface of the photosensitive drum 11 beyond the top of the flange 92. Therefore, when the drum unit 17 is pulled out, the flange 92 comes into contact with the film end portion 97A, and when the drum unit 17 is further pulled out, the film end portion 97A is bent. At this time, a reaction force due to the bending of the film end portion 97 </ b> A acts in a direction to move the flange 92 away from the developing roller 57. For this reason, when the drum unit 17 is pulled out from the apparatus main body 28, the photosensitive drum 11 is difficult to tilt toward the developing roller 57 side. As a result, the flange 92 is prevented from contacting the surface of the developing roller 57 and the gear portion 93 is prevented from contacting the surface of the developing roller 57.

  The film member 97 has an inclined portion 97B formed at a corner portion of the film end portion 97A on the insertion direction 8A side. The inclined portion 97B is a portion that contacts the inclined surface 92A of the flange 92 in the process in which the drum unit 17 is pulled out. When the drum unit 17 is pulled out, the inclined portion 97B comes into contact with the inclined surface 92A, so that the film member 97 is easily bent, and the burden on the film end portion 97A is reduced and the film member 97 is damaged. Is prevented.

  Since the second transmission gear 75 is configured as described above, the gear portion 93 of the second transmission gear 75 is prevented from coming into contact with the transfer surface of the transfer belt 23 when the drum unit 17 is pulled out from the apparatus main body 28. Is done. As a result, contamination or damage to the transfer belt 23 due to the contact of the gear portion 93 is prevented.

  In addition, since the film member 97 is provided as described above, the drum unit 17 is difficult to tilt toward the developing roller 57 in the process of being pulled out of the apparatus main body 28, and the flange 92 and the gear portion 93 are connected to the developing roller 57. It stops touching. As a result, the surface of the developing roller 57 is prevented from having streak marks or scratches.

  In the above-described embodiment, the film member 97 is exemplified as an example of the elastic member. However, an elastic member such as a sponge member or a rubber member can be applied instead of the film member 97.

10: Image forming apparatus 11: Photoconductor drum 15: Cleaning device 75: Second transmission gear 91: Fitting portion 92: Flange 93: Gear portion 94: Shaft portion 97: Film member

Claims (8)

A transfer belt provided in the apparatus body and having a transfer surface onto which a toner image is transferred;
A photosensitive drum that is detachably provided in the apparatus main body, is formed in a cylindrical shape having an insertion direction with respect to the apparatus main body as an axial direction, and faces the transfer surface of the transfer belt in a mounted state mounted on the apparatus main body. When,
A transmission member attached to a drum end of the photosensitive drum on the insertion direction side and transmitting an input rotational driving force to the photosensitive drum;
The transmission member is
A flange formed to an outer diameter larger than the outer diameter of the photosensitive drum;
A gear that protrudes from the flange in the insertion direction and has teeth that receive the rotational driving force on an outer peripheral surface, and is formed to have an outer diameter that is larger than the outer diameter of the photosensitive drum and smaller than the outer diameter of the flange; An image forming apparatus.   2. The flange according to claim 1, wherein the flange is not in contact with a belt end portion of the transfer belt in the insertion direction in the mounted state, and contacts the belt end portion in a process in which the photosensitive drum is pulled out from the apparatus main body. The image forming apparatus described.   The image forming apparatus according to claim 2, wherein the flange includes an inclined surface that is inclined with respect to the belt end. A developing roller rotatably supported so as to face the outer peripheral surface of the photosensitive drum with a predetermined gap therebetween;
An elastic member that is provided closer to the transfer belt than the developing roller, is in non-contact with the flange in the mounted state, and contacts the flange in the process of pulling out the photosensitive drum from the apparatus main body. The image forming apparatus according to claim 1.   The image forming apparatus according to claim 4, wherein the elastic member is a film member having elasticity that extends in an axial direction of the developing roller.   The image forming apparatus according to claim 4, wherein the elastic member has an inclined portion that can contact the flange at an end portion on the insertion direction side.   The image forming apparatus according to claim 4, wherein the elastic member extends toward the photosensitive drum side from an end portion in a radial direction of the flange in the mounted state.   The developing roller is provided at both ends in the axial direction of the developing roller, presses the both end portions of the outer peripheral surface of the photosensitive drum with a predetermined urging force, and sets the developing roller at a position spaced apart from the photosensitive drum by the predetermined gap. The image forming apparatus according to claim 4, further comprising a rotary roller for positioning.

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